Conventionally, a sound collecting device which generates signals (multichannel signals) corresponding to a plurality of channels by using a plurality of microphones, which signals re-create (realize sound image localization), at a transmission destination, a position of a sound source (for example, a speaker) at a transmission source, is used in an acoustic system such as a television conference system.
The plurality of microphones of the above sound collecting device are provided so as to correspond to the respective channels. In addition, the plurality of microphones are fixedly placed so as to concentrate at one position such that the main axes of the directionalities of the plurality of microphones are directed in the directions corresponding to the respective channels. Thus, the sound collecting device can generate sound collection signals as multichannel signals realizing sound image localization. The generated multichannel signals are transmitted, via a communication network, to a plurality of loudspeakers at a transmission destination. Thus, a multichannel sound is reproduced at the transmission destination, and the position of a speaker at the transmission source is re-created at the transmission destination.
Here, in order to generate multichannel signals realizing sound image localization, the plurality of microphones need to be fixedly placed such that the main axes of the directionalities of the plurality of microphones are directed in the directions corresponding to the respective channels. Therefore, the above sound collecting device does not allow a speaker to freely change the positions at which the plurality of microphones are placed.
Accordingly, a sound collecting device 9 as shown in FIG. 14 and FIG. 15 is supposed in order to solve the above problem (for example, Patent Document 1). FIG. 14 is a diagram showing a part of a configuration of equipment in a television conference system at a transmission source. FIG. 15 is a diagram showing in detail a circuitry configuration in the television conference system at the transmission source. In FIG. 14 and FIG. 15, as an example, an R-channel signal and an L-channel signal are generated as multichannel signals, and then stereo reproduction is realized at the transmission destination.
A microphone 90-1 is provided on a table 3 so as to be positioned in the vicinity of and in front of a speaker 2-1. A microphone 90-2 is provided on the table 3 so as to be positioned in the vicinity of and in front of a speaker 2-2. A monitor 4 is an apparatus for displaying a video image shot by a camera 5a at the transmission destination, and is provided in front of the speakers 2-1 and 2-2. The video image from the transmission destination is inputted to the monitor 4 via a communication network 7. A camera 5 is an apparatus for shooting the speakers 2-1 and 2-2 present at the transmission source, and is provided above the monitor 4. A video image shot at the transmission source is transmitted to a monitor 4a at the transmission destination via a communication network 7. Loudspeakers 6-1 and 6-2 are devices for respectively reproducing the L-channel signal (Lch) and the R-channel signal (Rch) which are inputted via the communication network 7 from a sound collecting device 9a at the transmission destination, and the loudspeakers 6-1 and 6-2 are provided on the both sides of the monitor 4. A loudspeaker 6a-1 at the transmission destination, which is not shown, is provided in front of a speaker at the transmission destination, and to the left as viewed from the speaker. A loudspeaker 6a-2 at the transmission destination, which is not shown, is provided in front of the speaker at the transmission destination, and to the right as viewed from the speaker.
A sound collecting device 9 is provided at the transmission source, and the sound collecting device 9a is provided at the transmission destination. The sound collecting device 9a has the same circuitry configuration as the sound collecting device 9, and the description of the sound collecting device 9a is omitted here. The sound collecting device 9 includes the microphones 90-1 and 90-2, microphone position measurement means 91, coefficient calculation means 92, microphone detection means 93, and signal calculation means 94. Hereinafter, components of the sound collecting device 9 will be described specifically.
The microphone position measurement means 91 outputs a measurement signal to the loudspeakers 6-1 and 6-2. Thereafter, the microphone position measurement means 91 calculates, as a delay time, a time period from when the measurement signal is outputted to when the measurement signal has been collected by the microphones 90-1 and 90-2. The microphone position measurement means 91 measures, from the calculated delay time, the current positions of the microphones 90-1 and 90-2. In FIG. 14, since the microphone 90-1 is placed at a position to the right as viewed from the monitor 4, the position to the right is measured as the current position of the microphone 90-1. In addition, since the microphone 90-2 is placed at a position to the left as viewed from the monitor 4, the position to the left is measured as the current position of the microphone 90-2. Note that, in order that a speaker can freely move the microphones 90-1 and 90-2, the microphone position measurement means 91 measures the current positions of the microphones 90-1 and 90-2 every time the microphones 90-1 and 90-2 are moved.
The coefficient calculation means 92 calculates a ratio (coefficient ratio) of a level to be allocated to the R-channel signal and a level to be allocated to the L-channel signal such that multichannel signals realizing sound image localization are generated based on the measured current positions of the microphones 90-1 and 90-2. In FIG. 14, the measured current position of the microphone 90-1 is a position to the right as viewed from the monitor 4. Therefore, the coefficient calculation means 92 calculates, for example, (R-channel signal:L-channel signal)=(1:0) as a coefficient ratio for the microphone 90-1. On the other hand, the measured current position of the microphone 90-2 is a position to the left as viewed from the monitor 4. Therefore, the coefficient calculation means 92 calculates, for example, (R-channel signal:L-channel signal)=(0:1) as a coefficient ratio for the microphone 90-2.
When either one of the speakers 2-1 and 2-2 speaks, the microphone detection means 93 detects a microphone nearest to the speaking speaker, based on the levels of sound collection signals from the microphones 90-1 and 90-2. For example, when the speaker 2-1 speaks, the level of the sound collection signal from the microphone 90-1 is larger than the level of the sound collection signal from the microphone 90-2. In this case, the microphone detection means 93 detects the microphone 90-1 as a microphone nearest to the speaking speaker. Thereafter, based on the microphone 90-1 detected by the microphone detection means 93, the coefficient calculation means 92 determines, as a coefficient ratio to be outputted to the signal calculation means 94, the coefficient ratio (R-channel signal:L-channel signal)=(1:0) calculated for the microphone 90-1.
The signal calculation means 94 calculates the R-channel signal and the L-channel signal in accordance with the determined coefficient ratio. For example, it is assumed that the coefficient ratio calculated for the microphone 90-1 is (R-channel signal:L-channel signal)=(1:0). In this case, the signal calculation means 94 calculates the R-channel signal by: multiplying each of the sound collection signals of the microphones 90-1 and 90-2 by coefficient “1”; and then summing the sound collection signals. On the other hand, the signal calculation means 94 calculates the L-channel signal by: multiplying each of the sound collection signals of the microphones 90-1 and 90-2 by coefficient “0”; and then summing the sound collection signals. As a result, the R-channel signal is a signal obtained by summing full sound collection signals from the microphones 90-1 and 90-2, and the L-channel signal is at zero level. Thus, the multichannel signals realizing sound image localization are generated. The L-channel signal (Lch) and the R-channel signal (Rch) calculated by the signal calculation means 94 are transmitted, via the communication network 7, respectively to the loudspeakers 6a-1 and 6a-2 at the transmission destination. Thus, reproduction is performed at the transmission destination such that a speaker at the transmission destination hears the speaker 2-1 speaking from a position to the right as viewed from the speaker at the transmission destination.
As described above, every time a microphone is moved, the sound collecting device 9 shown in FIG. 14 and FIG. 15 measures a position (current position) of the moved microphone, and generates multichannel signals realizing sound image localization by using information about the measured current position of the moved microphone. Therefore, the speaker can freely change a position at which the microphone is placed.
Patent Document 1: Japanese Laid-Open Patent Publication No. H9-182044 (FIG. 1, FIG. 2, etc.)